This invention relates to improvements in or relating to a method of and an apparatus for the nondestructive testing the internal pressure of sealed containers for canned goods, sealed containers for canned refreshments, widemouthed sealed bottles having metal caps, etc.
When a force of impact is applied to the wall of a sealed container, natural vibration is generated by the oscillation system unless the wall of the sealed container is nonresilient. Such natural vibration is closely related to the internal pressure of the vessel, although it may vary depending on the shape and material of the vessel to a certain extent. Proposals have already been made to carry out nondestructive testing of sealed containers based on this principle to determine whether or not the internal pressure of the sealed vessels is at an acceptable level.
Some disadvantages are associated with a method of the prior art for determining the level of the internal pressure of a sealed container by applying a force of impact thereto. The present practice is to apply a single pulse to the wall of a sealed container to obtain a response. Generally, the response made by the wall of a sealed container to the force of impact applied thereto tends to be reduced in energy with time. Thus difficulties have hitherto been experienced, when the method of the prior art of using a single pulse is relied on, in obtaining satisfactory results of tests because of the relatively short period of time during which the vibration to be measured exists.